Axial piston pump with piston having passive cooling thermal relief feature

ABSTRACT

A piston pump includes a rotor member with a bore therein. The bore is defined by an inner surface. The piston pump also includes a piston supported for reciprocating movement in an axial direction within the bore to change a volume of a pump chamber that is cooperatively defined by the piston and the rotor member. The piston has an outer surface that faces the inner surface with a leakage interface defined therebetween. The leakage interface is configured to receive a passive leakage flow of a fluid from the pump chamber through the leakage interface to provide cooling. Moreover, the outer surface includes a relief feature that is recessed into the outer surface to define, with the inner surface, a cooling pocket of the leakage interface. The cooling pocket moves in the axial direction relative to the inner surface with the reciprocating movement of the piston.

TECHNICAL FIELD

The present disclosure generally relates to a piston pump and, more particularly, relates to an axial piston pump with one or more pistons that include a passive cooling relief feature.

BACKGROUND

There are various types of pumps configured for pumping fluids. For example, there are various types of positive displacement, continuous travel piston pumps that have been developed for various uses.

A piston pump can generate significant frictional heating during operation. The sliding motion of the pistons can generate heat that may limit the usefulness of the pump. Some of these pumps may be inappropriate for pumping certain fluids because of the heat generated.

Active cooling systems may be included to address these problems. For example, some hydraulic fluid pumps include coolant lines or ports that provide a flow of coolant fluid. Although these active cooling systems can cool the pump, there may be a significant amount of leakage flow, resulting in a noticeable decrease in the pump volumetric efficiency. Including these active cooling systems can also increase manufacturing costs and complexity of the pump.

Accordingly, it is desirable to provide a piston pump that is useful for pumping a variety of fluids. It is also desirable to provide a piston pump that provides cooling in a wide variety of operating conditions while also preserving high volumetric efficiency. Moreover, it is desirable to provide manufacturing improvements for these pumps. Other desirable features and characteristics of the present disclosure will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background discussion.

BRIEF SUMMARY

In one embodiment, a piston pump is disclosed that is configured to displace a fluid. The piston pump includes a rotor member with a bore therein. The bore is defined by an inner surface. The piston pump also includes a piston supported for reciprocating movement in an axial direction within the bore to change a volume of a pump chamber that is cooperatively defined by the piston and the rotor member. The piston has an outer surface that faces the inner surface with a leakage interface defined therebetween. The leakage interface is configured to receive a passive leakage flow of the fluid from the pump chamber through the leakage interface to provide cooling. Moreover, the outer surface includes a relief feature that is recessed into the outer surface to define, with the inner surface, a cooling pocket of the leakage interface. The cooling pocket moves in the axial direction relative to the inner surface with the reciprocating movement of the piston.

In another embodiment, a method of operating an axial piston pump is disclosed. The method includes providing a rotor member with a bore therein. The bore is defined by an inner surface. The method also includes selectively moving a piston reciprocally in an axial direction within the bore to move a fluid through a pump chamber that is cooperatively defined by the piston and the rotor member. The piston has an outer surface that faces the inner surface with a leakage interface defined between the outer surface of the piston and the inner surface of the rotor member. The outer surface includes a relief feature that is recessed into the outer surface to define, with the inner surface, a cooling pocket of the leakage interface. Furthermore, the method includes passively leaking the fluid from the pump chamber and through the leakage interface as the cooling pocket moves in the axial direction relative to the inner surface with the reciprocating movement of the piston.

In a further embodiment, an axial piston pump is disclosed that is configured to displace an engine fuel. The pump includes a housing with an internal space therein. The pump also includes a rotor member with a bore therein. The bore is defined by an inner surface, and the rotor member supported for rotation about a longitudinal axis within the internal space. The pump further includes a piston supported for reciprocating movement along a bore axis within the bore to change a volume of a pump chamber that is cooperatively defined by the piston and the rotor member. The bore axis is parallel to the longitudinal axis, and the piston has an outer surface that faces the inner surface with a leakage interface defined therebetween. The leakage interface is configured to receive a passive leakage flow of the engine fuel from the pump chamber through the leakage interface to provide cooling. The outer surface includes a relief groove that is recessed into the outer surface. The relief groove separates a first adjacent area of the outer surface and a second adjacent area of the outer surface. The relief groove has a first shoulder that is substantially perpendicular to the bore axis and a second shoulder that is substantially perpendicular to the bore axis. The relief groove defines, with the inner surface, a cooling pocket of the leakage interface. The cooling pocket moves in the axial direction relative to the inner surface with the reciprocating movement of the piston. The cooling pocket remains within the bore throughout a stroke of the piston as the piston reciprocates.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:

FIG. 1 is a longitudinal cross-section view of an axial piston pump of a pump system according to example embodiments of the present disclosure;

FIG. 2 is an isometric longitudinal cross-section view of a piston and a rotor member of the axial piston pump of FIG. 1;

FIG. 3 is a longitudinal cross-section view of a cooling relief feature of the piston of FIG. 2 according to example embodiments of the present disclosure;

FIG. 4 is an isometric view of a ported member of the axial piston pump of FIG. 1; and

FIGS. 5-12 are schematic views of the axial piston pump illustrating operation of the pump.

The drawings are not necessarily drawn to scale unless otherwise noted.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and is not intended to limit the present disclosure or the application and uses of the present disclosure. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description.

Broadly, example embodiments disclosed herein include pump systems with a piston pump, such as an axial piston pump, having improved cooling features. One or more pistons of the pump may include a relief feature. The relief feature may be a groove, notch, or other feature recessed slightly into the outer surface (outer diameter surface) of the piston. As such, the piston outer surface may have one diameter at the relief feature and a larger diameter at other regions adjacent thereto. Conversely, the bore inner surface (inner diameter surface) may be continuous and smooth in regions that oppose the relief feature. Thus, the bore inner diameter may remain substantially constant along a majority of its length.

A leakage flow path may be defined between the outer surface of the piston and the bore inner surface. The pumped fluid may leak from the pump chamber and along the leakage flow path. The relief feature and the bore inner surface of the rotor member may cooperate to define a cooling pocket along the leakage flow path. The cooling pocket moves with the piston and reciprocates within the bore during operation of the pump. The cooling pocket may be positioned on the piston such that the relief feature remains within the length of the bore for the stroke of the piston. A minimal amount of leakage may be allowed along the piston/rotor interface, thus minimizing pump losses in volumetric efficiency while providing a localized reservoir of cooling fluid at predetermined areas of the interface.

The relief feature included on the pistons can maintain fluid film at the piston/rotor member sliding interface while providing cooling. The leakage flow provided by the relief feature has minimal impact on pump volumetric efficiency while still maintaining the local interface at temperatures within an allowable range. The relief feature resupplies the lubrication film during movement of the piston, reducing its overall temperature and disrupting localized hot spots in the film.

The leakage flow may be a passive flow of the fluid along the interface. As such, flow may occur in concert with and/or because of the reciprocating movement of the piston. Stated differently, actively pumping additional cooling fluid across the interface and/or through the piston wall is unnecessary. In other words, there need not be dedicated feed lines to the relief feature or drain lines from the relief features. Instead of actively supplying cooling fluid to the relief feature, it is resupplied by the motion of the piston in the bore. Accordingly, the passively cooling pump of the present disclosure has high efficiency. The pump of the present disclosure also provides manufacturing efficiencies as well.

Furthermore, the pump may be utilized for pumping a wide variety of fluids. In some embodiments, the pump may be used to pump a low-lubricity fluid, such as fuel for an engine. In additional embodiments, the pump may be used or for pumping actuator fluid for an actuator.

Referring now to FIG. 1, example embodiments of a pump system 100 will be discussed. The pump system 100 may include or comprise a pump 101 for selectively pumping a fluid therethrough. The pump 101 may be a positive displacement, continuous travel, piston pump. Specifically, the pump 101 may comprise an axial piston pump. However, it will be appreciated that one or more features of the present disclosure may apply to other piston pumps, such as a bent axis piston pump or a radial piston pump.

In some embodiments, the pump 101 may be used for pumping fuel. For example, the pump 101 may be included on a vehicle, such as an aircraft, and the pump 101 may pump fuel to an engine thereof. In some embodiments, the pump 101 may be configured as a main engine fuel pump. In additional embodiments, the pump 101 may be configured for pumping fluid for a hydraulic actuator.

Generally, the pump 101 may include a housing 102 that defines a longitudinal axis 104. The pump 101 also generally includes a rotating group 106 supported for rotation about the axis 104 within the housing 102. The rotating group 106 generally includes a rotor member 108 supported for rotation about the axis 104 and a plurality of pistons (e.g., a first piston 112 and a second piston 113) that are moveably supported by the rotor member 108. The first piston 112 and the second piston 113 are shown in FIG. 1, but it will be appreciated that the rotating group 106 may include any suitable number of pistons spaced apart circumferentially about the axis 114. The pistons 112, 113 may be received in respective bores 144 of the rotor member 108 and may slide axially along a respective bore axis 114. The pistons 112, 113 may be coupled to a cam retainer 156 (or a hanger in the case of a variable displacement pump) and a cam plate 158 of the rotor member 108, which are disposed at a non-orthogonal angle 141 (i.e., a cam angle) relative to the axis 104.

As will be described in detail below, the pistons 112, 113 may reciprocate axially along the respective bore axis 114 as the rotor member 108 rotates about the axis 104. It is noted that the bore axes 114 may be arranged parallel to the axis 104 (the centerline axis) of the shaft 140. This motion may cause the pistons 112, 113 to draw fluid into the respective bore 144 from a fluid intake system 116 and subsequently expel the fluid to a discharge system 118. The fluid intake system 116 may provide fuel to the pump 101 (e.g., from a fuel tank). The pump 101 may provide pressurized fluid to an engine, an actuator, or other device via the discharge system 118. Thus, the pump 101 may drive flow of the fluid through the system 100.

The housing 102 will now be discussed according to example embodiments. The housing 102 may include one or more rigid and strong components that support movement of the rotating group 106. The housing 102 may also house, contain, enclose, and/or encapsulate the rotating group 106 therein. The housing 102 may include a head 120 and a housing body 122. The housing body 122 may be a hollow, rigid member that includes a radial feature 124 and a longitudinal end 126. The head 120 may cover over and fixedly attach to the housing body 122 in a position that is longitudinally opposite the end 126. Accordingly, the head 120, the radial feature 124, and the end 126 may collectively define an internal space 128. The internal space 128 may be substantially cylindrical. The internal space 128 may be sealed off via one or more seals (e.g., between the head 120 and the housing body 122). The internal space may also include a fluid inlet 134 and a fluid outlet 136. In some embodiments, the end 126 may include one or more apertures that define the fluid inlet 134 and one or more apertures that define the fluid outlet 136. The fluid inlet 134 may be in fluid communication with the intake system 116, and the fluid outlet 136 may be in fluid communication with the discharge system 118.

Referring now to FIGS. 1 and 2, the rotating group 106 will be discussed in greater detail. The rotor member 108 of the rotating group 106 may include a shaft 140 that is centered on the axis 104. The rotor member 108 may also include a disc- or puck-shaped rotor body 142, which is fixed to one end of the shaft 140. The rotor member 108 may include a plurality of insert sleeves 151 that are removably and fixedly attached to the rotor body 142. The insert sleeves 151 may be hollow, cylindrical tubes. An inner surface 146 (inner diameter surface) of the sleeve 151 may define the respective bore 144 of the rotor member 108. As shown in FIG. 2, the plurality of bores 144 extend along the respective bore axis 114 and include a proximal end 150 and a distal end 152.

As shown in FIG. 1, the rotating group 106 may be supported for rotation within the housing 102 by one or more bearings 154. At least one bearing 154 may support the shaft 140 on the head 120 and at least one other bearing 154 may support the rotor body 142 on the housing body 122. Accordingly, the rotating group 106 may be supported for rotation within the internal space 128 of the housing 102. The bores 144 may be oriented with the respective distal ends 152 oriented toward the longitudinal end 126 of the housing 102. As will be discussed, the distal ends 152 may rotate about the axis 104 with rotation of the rotating group 106. Also, the distal ends 152 may be open and may intermittently connect to the fluid inlet 134 and, alternatively, to the fluid outlet 136 as the rotating group 106 rotates within the housing 102.

The pump 101 may also include the cam retainer 156, which is fixed to the housing 102, and which encircles the shaft 140. The pump 101 may also include the cam plate 158, which is supported by the cam retainer 156. The cam plate 158 may be disposed at the non-orthogogonal cam angle 141 relative to the axis 104.

The first piston 112 is shown in detail in FIG. 2 as an example and may be representative of the second piston 113 as well as any additional pistons of the rotating group 106. As shown in FIG. 2, the piston 112 may be elongate and may extend longitudinally along the respective bore axis 114 between a first end 162 and a second end 166. The first end 162 may be rounded. The piston 112 may also include a hollow, cylindrical wall 115 that extends longitudinally from the first end 162 to define the second end 166. The wall 115 may terminate at an open, annular terminal end 168 (a second terminal end of the piston 112). The wall 115 defines a cylindrical outer surface 160 (e.g., an outer diameter surface). The wall 115 of the piston 112 may also include an inner cavity 161 defined by inner surface 163 (e.g., an inner diameter surface). The inner cavity 161 may be defined at one end by an inner longitudinal end 109 and may be open at the opposite longitudinal end.

The piston 112 may be disposed in the respective bore 144 with the first end 162 of the piston 112 disposed proximate the proximal end 150. The first end 162 may be received in a shoe 164, which is loaded against the cam plate 158. Also, the second end 166 of the piston 112 may be disposed proximate the distal end 152 of the bore 144.

The piston 112 and the rotor member 108 cooperatively define a pump chamber 170. Specifically, the pump chamber 170 may be defined by the inner surface 163 and the terminal end 168 of the piston 112 in cooperation with the inner surface 146 of the bore 144 at the distal end 152. The pump chamber 170 may be fluidly connected to the internal space 128 of the housing 102. Stated differently, the pump chamber 170 may be open at the distal end 152 of the bore 144. As such, the pump chamber 170 may intermittently connect to the fluid inlet 134 and, alternatively, to the fluid outlet 136 as the rotating group 106 rotates within the housing 102.

As mentioned, the piston 112 may be supported for reciprocating sliding movement in an axial direction within the bore 144. This changes a volume of the pump chamber 170. Specifically, as the rotating group 106 rotates about the axis 104, the shoe 164 pushes the first end 162 of the piston 112 circumferentially about the axis 104, and the cam plate 158 cams against the first end 162 to reciprocate the piston 112 axially along its respective bore axis 114, in and out of the proximal end 150 of the bore 144. Meanwhile the second end 166 of the piston moves toward and away from the distal end 152 of the bore 144 as the rotating group 106 rotates about the axis 104.

A stroke of the piston 112 is illustrated in FIG. 2. As shown, the second terminal end 168 is shown in solid lines to demonstrate a first axial position of the piston 112 within the bore 144 with respect to the axis 114. In some embodiments, this first axial position may be the bottom dead center position of the piston 112. The second terminal end 168 is shown in phantom lines to demonstrate a second axial position of the piston 112 within the bore 144. In some embodiments, this second axial position may be the top dead center position of the piston 112. The piston 112 may reciprocate between these two axial positions as indicated by arrow 107. The stroke (i.e., stroke length, stroke zone, etc.) of the piston 112 is the axial distance (measured along the axis 114) between the two positions. Thus, the stroke is the distance that the piston 112 travels as it moves between the two positions. The piston 112 may complete the stroke as the rotating group 106 completes a single rotation around the axis 104.

The pump 101 may further include a ported member 184 (i.e., a port plate). As shown in FIG. 4, the ported member 184 may be a rounded plate with a disc-like shape. As shown in FIG. 1, the ported member 184 may be disposed between the rotating group 106 and the end 126 of the housing 102. The ported member 184 may include a first face 186 that faces the rotating group 106 and a second face 188 that faces the end 126 of the housing 102. The ported member 184 may further include an outer edge 189 that faces the radial feature 124 of the housing 102. The ported member 184 may be nested within the housing 102 proximate the fluid inlet 134 and the fluid outlet 136.

Furthermore, the ported member 184 may include at least one intake port 190. The intake port 190 may be arcuate (e.g., kidney-shaped) and may extend partially about the axis 104. The intake port 190 may define a passage through the ported member 184 between the first face 186 and the second face 188 of the ported member 184. In some embodiments, there may be plural, individual passages that extend from the first face 186 to the second face 188 with different surface features configured to direct flow of fluid (e.g., fuel) through the ported member 184 from the second face 188 to the first face 186. The ported member 184 may be disposed within the housing 102 with the intake port 190 aligned with and in fluid communication with the fluid inlet 134. Moreover, the intake port 190 may be disposed substantially at the same radius as the pistons 112, 113 relative to the axis 104. Thus, the pistons 112, 113 may draw flow through the intake port 190 when the pistons 112, 113 come into alignment with the intake port 190. In other words, the intake port 190 temporarily fluidly connects the fluid inlet 134 and the pump chamber 170 of the first piston 112 as the rotating group 106 rotates within the internal space 128. The intake port 190 likewise temporarily fluidly connects the fluid inlet 134 and the pump chamber 170 of the second piston 113 as well as the other pistons as they rotate about the axis 104 with rotation of the rotating group 106.

Additionally, the ported member 184 may include at least one discharge port 192. The discharge port 192 may be arcuate (e.g., kidney-shaped) and may extend partially about the axis 104. The discharge port 192 may be spaced on an opposite side of the axis 104 from the intake port 190. The discharge port 192 may also extend between the first face 186 and the second face 188 of the ported member 184. The ported member 184 may be disposed within the housing 102 with the discharge port 192 aligned with and in fluid communication with the fluid outlet 136. Moreover, the discharge port 192 may be disposed substantially at the same radius as the pistons 112, 113 relative to the axis 104. Thus, the pistons 112, 113 may discharge fluid via the discharge port 192 when the pistons 112, 113 come into alignment with the discharge port 192. In other words, the discharge port 192 temporarily fluidly connects the pump chamber 170 of the first piston 112 and the fluid outlet 136 as the rotating group 106 rotates within the internal space 128. The discharge port 192 likewise temporarily fluidly connects the pump chamber 170 of the second piston 113 and the fluid outlet 136 and the other pistons as they rotate about the axis 104 with rotation of the rotating group 106.

Moreover, the ported member 184 may include a first balance aperture 194. The first balance aperture 194 may be a passage that extends from the first face 186 to the second face 188. As shown in FIG. 1, the first balance aperture 194 may include a feed portion 196 and a cavity portion 198. The feed portion 196 may extend from the first face 186 and may have a smaller width (e.g., a smaller diameter) than the cavity portion 198. The cavity portion 198 may be open at the second face 188. As shown in FIG. 4, the first balance aperture 194 may be circumferentially spaced between the intake port 190 and the discharge port 192. The first balance aperture 194 may be configured to pass fluid in a thickness direction through the ported member 184, between the first face 186 and the second face 188.

Still further, the ported member 184 may include a second balance aperture 200. The second balance aperture 200 may be a passage that extends from the first face 186 to the second face 188. As shown in FIG. 1, the second balance aperture 200 may include a feed portion 202 and a cavity portion 204. The feed portion 202 may extend from the first face 186 and may have a smaller width (e.g., a smaller diameter) than the cavity portion 204. The cavity portion 204 may be open at the second face 188. As shown in FIG. 4, the second balance aperture 200 may be circumferentially spaced between the intake port 190 and the discharge port 192. The second balance aperture 200 may be spaced on the opposite side of the axis 104 (e.g., approximately one hundred eighty degrees (180°)) from the first balance aperture 194. The second balance aperture 200 may be configured to pass fluid in a thickness direction through the ported member 184, between the first face 186 and the second face 188.

The ported member 184 may be received within the internal space 128 between the rotating group 106 and the end 126 of the housing 102. In some embodiments, the ported member 184 may “float” within this space between the rotating group 106 and the end 126 of the housing 102.

The ported member 184 may have a neutral position within the space 128. The ported member 184 may be substantially orthogonal to the axis 104 when in the neutral position. Also, the intake port 190 may be aligned with the fluid inlet 134 and the discharge port 192 may be aligned with the fluid outlet 136 when in the neutral position. The ported member 184 is moveably disposed (i.e., “floats”) within the space 128. During operation of the pump 101, forces may tend to push the ported member 184 away from the neutral position and toward an unbalanced position. More specifically, these forces may tend to tilt the ported member 184 slightly to a non-orthogonal angle relative to the axis 104.

However, the pump 101 may include a first biasing member 207 and a second biasing member 209, which create a counter-balancing force for biasing the ported member 184 toward the neutral position. The first and second biasing members 207, 209 may create a counter-moment for maintaining the ported member 184 substantially orthogonal to the axis 104. The first biasing member 207 may be a substantially cylindrical member that is received in the cavity portion 198 of the first balance aperture 194. The size and shape of the first biasing member 207 may correspond substantially to that of the cavity portion 198. Likewise, the second biasing member 209 may be a substantially cylindrical member that is received in the cavity portion 204 of the second balance aperture 200. The size and shape of the second biasing member 209 may correspond substantially to that of the cavity portion 204. During operation, the pump chambers 170 of the pistons 112, 113 may intermittently connect fluidly to the first balance aperture 194 (e.g., in the position shown in FIGS. 7 and 8), and the pump chambers 170 of the pistons 112, 113 may intermittently connect fluidly to the second balance aperture 200 (e.g., in the position shown in FIGS. 11 and 12). In these positions, fluid may move between the pump chambers 170 and the balance apertures 194, 200 such that the biasing members 207, 209 bias the ported member 184 toward the balanced, neutral position within the internal space 128 as the rotating group 106 rotates therein.

The pump system 100 may further include a control system 206 (FIG. 1). The control system 206 may control various features of the pump 101. The control system 206 may be a computerized system, for example, with one or more processors, memory elements, input and output devices, etc. Also, the control system 206 may include and/or incorporate at least one actuator 208. The actuator(s) 208 may include one or more fluid actuators, pneumatic actuators, electric actuators, etc. The actuator(s) 208 may include a shaft actuator for rotating the shaft 140. Additionally, the actuator(s) 208 may include a cam actuator for actuating the cam plate 158, for example, for selectively changing the angle 141 (e.g., in a variable displacement pump configuration). Stated differently, although the pump 101 illustrated in FIG. 1 is a fixed displacement pump, the pump 101 may be configured as a variable displacement pump wherein the actuator 208 actuates to change the angle 141. Changing the angle 141 changes the stroke length of the pistons 112, 113 during a single rotation of the rotating group 106 about the axis 104. The control system 206 may receive inputs, such as input from a sensor, that detects an operating condition and/or that distinguishes between different operating conditions. As mentioned above, the pump system 100 may be incorporated as a fuel pump for an engine in some embodiments. In this case, the control system 206 may receive sensor input indicating a throttle position, a user request, and/or other input. The control system 206 may process the input and, in turn, generate control signals for the actuator(s) 208 according to the processed input. For example, the actuator 208 may change the speed of the shaft 140 according to control signals sent from the control system 206. In the case of a variable displacement pump 101, the control system 206 may command the actuator 208 to change the angle 141.

Rotation of the shaft and the position of the piston 112 relative to the ported member 184 is shown schematically in FIGS. 5-12. The first piston 112 is illustrated, but it will be appreciated that the second piston 113 and/or the others of the pistons may operate similarly. The direction of rotation of the piston 112 about the axis 104 relative to the ported member 184 is indicated with arrow 105.

Beginning, for example, at the circumferential position of the piston 112 represented in FIGS. 5 and 6, the pump chamber 170 of the first piston 112 may be aligned with the intake port 190 of the ported member 184 (i.e., moves circumferentially between the arcuate ends of the intake port 190). The piston 112 may remain aligned with the intake port 190 and may continue to withdraw from the rotor member 108 as the rotating group 106 rotates, thereby drawing the fluid from the fluid inlet 134, through the intake port 190, and into the pump chamber 170. The piston 112 continues to advance in the circumferential direction to a first intermediate position represented in FIGS. 7 and 8. Then, as shown in FIGS. 9 and 10 the piston 112 rotates into alignment with the discharge port 192 (i.e., moves circumferentially between the arcuate ends of the discharge port 192) while advancing into the respective bore 144 to thereby discharge the fluid from the pump chamber 170 to the fluid outlet 136. The piston 112 continues to a second intermediate position represented in FIGS. 11 and 12. The rotational cycle continues with the piston 112 aligning with the intake port 190 (FIGS. 5 and 6) and so on during rotation of the rotating group 106.

In the first intermediate position of FIGS. 7 and 8, the pump chamber 170 is in fluid communication with the first balance aperture 194. As such, fluid may flow between the pump chamber 170 and the aperture 194. Fluid pressure causes the first biasing member 207 to bias the ported member 184 toward the balanced, neutral position within the internal space 128 (e.g., orthogonal to the axis 104) as the rotating group 106 rotates about the axis 104. Likewise, in the second intermediate position of FIGS. 11 and 12, the pump chamber 170 is in fluid communication with the second balance aperture 200. As such, fluid may flow between the pump chamber 170 and the aperture 200. Fluid pressure causes the second biasing member 209 to bias the ported member 184 toward the balanced, neutral position within the internal space 128 (e.g., orthogonal to the axis 104) as the rotating group 106 rotates about the axis 104.

Referring now to FIG. 2, the interface between the outer surface 160 of the piston 112 and the inner surface 146 of the bore 144 will be discussed. This interface may be referred to as a leakage interface 172 for the pumped fluid. The leakage interface 172 is defined axially from the terminal end 168 of the piston 112 to the proximal end 150 of bore 144 (from the pump chamber 170 to proximal end 150 of bore 144). The axial length of the leakage interface 172, as such, varies, with the reciprocation of the piston 112. The pump 101 may permit a minimal amount of fluid (e.g., fuel) to leak from the pump chamber 170 via the leakage interface 172. This may be a passive flow of fluid resulting from the pumping action of the piston 112. The fluid leaks from the pump chamber 170 and through the leakage interface 172 to provide cooling.

As shown in FIGS. 1-3, the piston 112 may include at least one relief feature 174. As shown, the relief feature 174 may be the sole (only) relief feature of the piston 112; however, the piston 112 may include a plurality of relief features 174 spaced apart longitudinally without departing from the scope of the present disclosure.

The relief feature 174 may be a groove, recess, moat, aperture, notch, rut, or other shallow feature that is recessed radially into the outer surface 160. As shown in FIG. 3, the relief feature 174 may have a substantially rectangular cross-sectional profile with a recess surface 191, a first end shoulder 176, and a second end shoulder 178. The first end shoulder 176 may be disposed closer to the first end 162, and the second end shoulder 178 may be disposed closer to the second end 166. One or both shoulders 176, 178 may be substantially perpendicular to the axis 114. (Those having ordinary skill in the art will understand that the term “substantially” is used in this context to account for the shoulders 176, 178 to be chamfered or otherwise treated to remove burrs or another sharpened edge during the manufacturing process.) The recess surface 191 may face outward radially and may be spaced inwardly (recessed) radially from adjacent areas 193 at a radial depth 177. As such, the shoulders 176, 178 may define opposite terminal ends of the relief feature 174. The relief feature 174 may have an axial length 175 measured parallel to the axis 114 from the first end shoulder 176 to the second end shoulder 178. The relief feature 174 may extend annularly and continuously about the outer surface 160 axis 114 such that the rectangular cross-sectional profile illustrated in FIG. 3 is constant about the circumference of the piston 112. As shown in the illustrated embodiments, the relief feature 174 may be the sole (only) relief feature 174 of the piston 112.

The depth 177 may be small and minimal relative to the radius of the piston 112 and/or relative to the wall thickness of the outer wall 115. The depth 177 measured at the recess surface 191 may be less than 1/20 of the radius at the area 193. In some embodiments, the depth 177 may be less than approximately 0.4% of the radius of the piston 112. In an example embodiment, the adjacent area 193 may have a radius of approximately 0.7722 inches, and the radius at the surface 191 may be approximately 0.7692 inches. Accordingly, the depth 177 may be approximately 0.003 inches in this example.

Furthermore, the relief feature 174 may be spaced apart from the second terminal end at a distance 182 measured in the axial direction. The distance 182 may be measured parallel to the axis 114 and from the terminal end 168 to the second end shoulder 178 as shown in FIG. 3. The length 175 of the relief feature 174 may be minimal relative to the overall length of the piston 112. For example, the length 175 may be less than 1/20 of the overall length of the piston 112. In the example embodiment, the length 175 may be approximately 0.2 inches, and the distance 182 may be approximately 0.5 inches.

The relief feature 174 may be formed in a variety of ways. For example, the relief feature 174 may be formed using a grinding operation (i.e., using a grinder machine 299 illustrated schematically in FIG. 3). For example, the piston 112 may be machined using a cutting machine (e.g., a lathe) in some embodiments. Then the outer surface 160 may be ground and/or polished using an appropriate grinder/polisher head of the grinder machine 299. Subsequently, the relief feature 174 may be formed with at least one additional pass of the head of the grinder machine 299.

As shown in FIGS. 1 and 2, the relief feature 174 defines a cooling pocket 180 of the leakage interface 172 in cooperation with the inner surface 146 of the bore 144. The inner surface 146 may be smooth and continuous in areas that oppose the relief feature 174. Accordingly, as shown, the cooling pocket 180 may have a rectangular cross-sectional profile. The inner surface 146 may be smooth, uninterrupted by holes or grooves, and may be disposed at a diameter that remains constant along the leakage interface 172. Accordingly, the inner surface 146 may be smooth and continuous (with a constant diameter) along the entire stroke length of the piston 112. In the case of a variable displacement pump where the stroke length is variable, the inner surface 146 may be smooth and continuous for the range of stroke lengths of the piston 112. Likewise, the adjacent areas 193 on either side of the relief feature 174 may be smooth, uninterrupted by holes or grooves, and may be disposed at a diameter that remains constant along the leakage interface 172. As the piston 112 reciprocates, the cooling pocket 180 moves in the axial direction relative to the inner surface 146 of the bore 144. In these examples, the coolant pocket 180 remains inside the bore 144 during reciprocating movement of the piston 112. This is shown in FIG. 2, wherein the coolant pocket 180 is shown in solid lines for the first axial position of the piston 112, and wherein the coolant pocket 180′ is shown in phantom lines for the second axial position of the piston 112.

The size, shape, and location of the relief feature 174 may be selected to provide cooling to predetermined areas of the leakage interface 172. In other words, there may be a known area on the outer surface 160 that is prone to heating, and the relief feature 174 may be formed at this area at a predetermined size and location to provide needed cooling. Fluid (e.g., fuel) may leak along the leakage interface 172 from the pump chamber 170 to the proximal end 150 of the bore 144, thereby cooling the interface 172. The cooling pocket 180 passively supplies this flow and enhances the cooling effect. The relief feature 174 maintains fluid film at the interface 172 while providing cooling. The leakage flow provided by the relief feature 174 has minimal impact on pump volumetric efficiency while still maintaining the interface 172 at temperatures within an allowable range. The relief feature 174 resupplies the liberation film during movement of the piston 112, reducing its overall temperature and disrupting localized hot spots in the film. Cooling, leakage flow may occur in concert with and/or because of the reciprocating movement of the piston for high efficiency operation of the pump 101. Furthermore, the relief feature 174 may be formed on the piston 112, and the pump 101 may be manufactured and assembled in a highly efficient manner. Moreover, these cooling features may allow the pump to be used for pumping a wide variety of fluids, such as fuel.

While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the present disclosure in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the present disclosure. It is understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the present disclosure as set forth in the appended claims. 

What is claimed is:
 1. A piston pump configured to displace a fluid comprising: a rotor member with a bore therein, the bore defined by an inner surface; a piston supported for reciprocating movement in an axial direction within the bore to change a volume of a pump chamber that is cooperatively defined by the piston and the rotor member, the piston having an outer surface that faces the inner surface with a leakage interface defined therebetween, the leakage interface configured to receive a passive leakage flow of the fluid from the pump chamber through the leakage interface to provide cooling; and the outer surface including a relief feature that is recessed into the outer surface to define, with the inner surface, a cooling pocket of the leakage interface, the cooling pocket moving in the axial direction relative to the inner surface with the reciprocating movement of the piston.
 2. The piston pump of claim 1, wherein the bore includes a proximal end and a distal end; wherein the piston includes a first end proximate the proximal end and a second end proximate the distal end; wherein the distal end of the bore and the second end of the piston cooperatively define at least part of the pump chamber; wherein the second end of the piston terminates at a second terminal end of the piston; and wherein the relief feature is spaced apart from the second terminal end at a distance measured in the axial direction.
 3. The piston pump of claim 2, wherein the outer surface of the piston includes a second end shoulder that defines a terminal end of the relief feature that is proximate the second end.
 4. The piston pump of claim 3, wherein the piston includes a first end shoulder that defines a first terminal end of the relief feature, the first end shoulder being spaced apart at a relief width dimension from the second end shoulder along the axial direction.
 5. The piston pump of claim 4, wherein the relief feature has a substantially rectangular cross-sectional profile.
 6. The piston pump of claim 2, wherein the second end is configured to move between a first axial point and a second axial point of the inner surface as the piston reciprocates within the bore; and wherein a stroke of the piston is defined between the first axial point and the second axial point in the axial direction; wherein the inner surface is smooth and continuous throughout the stroke of the piston.
 7. The piston pump of claim 6, wherein the relief feature remains inside the bore throughout the stroke of the piston.
 8. The piston pump of claim 1, wherein the fluid is an engine fuel.
 9. The piston pump of claim 1, wherein the rotor member and the piston are configured as an axial piston pump.
 10. The piston pump of claim 1, wherein the relief feature extends annularly and continuously about the outer surface of the piston.
 11. The piston pump of claim 10, wherein the relief feature is the sole relief feature of the piston.
 12. The piston pump of claim 1, wherein the rotor member includes a rotor body and an insert sleeve that is attached to the rotor body; and wherein the insert sleeve includes the inner surface.
 13. The piston pump of claim 1, wherein the relief feature is a groove recessed into the outer surface from a first adjacent area and a second adjacent area of the outer surface, the groove separating the first and second adjacent areas.
 14. The piston pump of claim 1, wherein the piston extends between a first end and a second end, wherein the piston includes a hollow and cylindrical wall that extends from the first end and defines the second end; and wherein the wall includes the outer surface that includes the relief feature.
 15. A method of operating an axial piston pump comprising: providing a rotor member with a bore therein, the bore defined by an inner surface; selectively moving a piston reciprocally in an axial direction within the bore to move a fluid through a pump chamber that is cooperatively defined by the piston and the rotor member, the piston having an outer surface that faces the inner surface with a leakage interface defined between the outer surface of the piston and the inner surface of the rotor member, the outer surface including a relief feature that is recessed into the outer surface to define, with the inner surface, a cooling pocket of the leakage interface; and passively leaking the fluid from the pump chamber and through the leakage interface as the cooling pocket moves in the axial direction relative to the inner surface with the reciprocating movement of the piston.
 16. The method of claim 15, further comprising: receiving, by a control system, sensor input from a sensor, the sensor input based on a condition detected by the sensor; and controlling, by the control system, an actuator based on the sensor input to change the reciprocating movement of the piston.
 17. The method of claim 15, wherein the bore includes a proximal end and a distal end; wherein the piston includes a first end proximate the proximal end and a second end proximate the distal end; wherein the distal end of the bore and the second end of the piston cooperatively define at least part of the pump chamber; wherein the second end of the piston terminates at a second terminal end of the piston; and wherein the relief feature is spaced apart from the second terminal end at a distance measured in the axial direction.
 18. The method of claim 17, wherein moving the piston includes moving the piston between a first axial point and a second axial point of the inner surface reciprocally within the bore to define a stroke between the first axial point and the second axial point, wherein the inner surface is smooth and continuous throughout the stroke of the piston.
 19. The method of claim 18, wherein moving the piston includes maintaining the relief feature inside the bore throughout the stroke of the piston.
 20. An axial piston pump configured to displace an engine fuel comprising: a housing with an internal space therein; a rotor member with a bore therein, the bore defined by an inner surface, the rotor member supported for rotation about a longitudinal axis within the internal space; a piston supported for reciprocating movement along a bore axis within the bore to change a volume of a pump chamber that is cooperatively defined by the piston and the rotor member, the bore axis being parallel to the longitudinal axis, the piston having an outer surface that faces the inner surface with a leakage interface defined therebetween, the leakage interface configured to receive a passive leakage flow of the engine fuel from the pump chamber through the leakage interface to provide cooling; and the outer surface including a relief groove that is recessed into the outer surface, the relief groove separating a first adjacent area of the outer surface and a second adjacent area of the outer surface, the relief groove having a first shoulder that is perpendicular to the bore axis and a second shoulder that is perpendicular to the bore axis, the relief groove defining with the inner surface, a cooling pocket of the leakage interface, the cooling pocket moving in the axial direction relative to the inner surface with the reciprocating movement of the piston, the cooling pocket remaining within the bore throughout a stroke of the piston as the piston reciprocates. 